Des Moines, July 24 -- Sometimes after a particularly grueling workout, sprinter Justin Gatlin will turn to his younger training partners and inquire: "Are you sore, too?"

It's just an age check. He doesn't feel 37 except on rare occasions. Like at big races when he sees so much youth on the starting line and not the familiar faces from years gone by.

Missing, of course, is his biggest rival, Usain Bolt, the Jamaican standout who rewrote the record book before saying goodbye to track nearly two years ago.

Arriving on the scene, a slew of 20-somethings such as Americans Christian Coleman and Noah Lyles who present another challenge for Gatlin , the defending 100-meter world champion.

"I don't think about age. I don't think about being ...